diff --git a/data/json/effects_on_condition/mutation_eocs/mutation_effect_eocs.json b/data/json/effects_on_condition/mutation_eocs/mutation_effect_eocs.json
index a025164fed4c6..0fd4be7584a0b 100644
--- a/data/json/effects_on_condition/mutation_eocs/mutation_effect_eocs.json
+++ b/data/json/effects_on_condition/mutation_eocs/mutation_effect_eocs.json
@@ -1,4 +1,9 @@
 [
+  {
+    "type": "effect_on_condition",
+    "id": "eoc_debug_mutate",
+    "effect": [ { "u_mutate": 0 } ]
+  },
   {
     "type": "effect_on_condition",
     "id": "mut_eyestalk",
diff --git a/data/json/mutations/mutations.json b/data/json/mutations/mutations.json
index 2a3eabbb17489..312b9c52ffc0c 100644
--- a/data/json/mutations/mutations.json
+++ b/data/json/mutations/mutations.json
@@ -5211,6 +5211,7 @@
     "prereqs": [ "WINGS_STUB" ],
     "prereqs2": [ "HOLLOW_BONES" ],
     "threshreq": [ "THRESH_BIRD" ],
+    "strict_threshreq": true,
     "category": [ "BIRD" ],
     "restricts_gear": [ "arm_l", "arm_r", "hand_l", "hand_r" ],
     "flags": [ "WINGS_2", "WING_GLIDE", "ARM_WINGS" ]
@@ -8126,7 +8127,8 @@
     "description": "You sometimes look back on your days before your tail came in.  But you're better now.",
     "valid": false,
     "purifiable": false,
-    "threshold": true
+    "threshold": true,
+    "threshold_substitutes": [ "THRESH_CHIMERA" ]
   },
   {
     "type": "mutation",
@@ -8137,7 +8139,8 @@
     "flags": [ "INVERTEBRATEBLOOD" ],
     "valid": false,
     "purifiable": false,
-    "threshold": true
+    "threshold": true,
+    "threshold_substitutes": [ "THRESH_CHIMERA" ]
   },
   {
     "type": "mutation",
@@ -8147,7 +8150,8 @@
     "description": "You're sure you'll fly someday.  In the meantime, there are still nests to build.",
     "valid": false,
     "purifiable": false,
-    "threshold": true
+    "threshold": true,
+    "threshold_substitutes": [ "THRESH_CHIMERA" ]
   },
   {
     "type": "mutation",
@@ -8157,7 +8161,8 @@
     "description": "Ninety percent of the planet, and it's yours to explore.  And colonize.  And enjoy.  What was that about a surface?",
     "valid": false,
     "purifiable": false,
-    "threshold": true
+    "threshold": true,
+    "threshold_substitutes": [ "THRESH_CHIMERA" ]
   },
   {
     "type": "mutation",
@@ -8167,7 +8172,8 @@
     "description": "It's about time you grew out.  Now that you've matured, it is time to make something of yourself.",
     "valid": false,
     "purifiable": false,
-    "threshold": true
+    "threshold": true,
+    "threshold_substitutes": [ "THRESH_CHIMERA" ]
   },
   {
     "type": "mutation",
@@ -8177,7 +8183,8 @@
     "description": "Stalking prey, eating well, and lying in the sun.  Mmm, all you could ever desire.",
     "valid": false,
     "purifiable": false,
-    "threshold": true
+    "threshold": true,
+    "threshold_substitutes": [ "THRESH_CHIMERA" ]
   },
   {
     "type": "mutation",
@@ -8187,7 +8194,8 @@
     "description": "You're the perfect candidate to lead a pack.",
     "valid": false,
     "purifiable": false,
-    "threshold": true
+    "threshold": true,
+    "threshold_substitutes": [ "THRESH_CHIMERA" ]
   },
   {
     "type": "mutation",
@@ -8197,7 +8205,8 @@
     "description": "So the humans died; what's the worry?  Now they won't ruin the woods.",
     "valid": false,
     "purifiable": false,
-    "threshold": true
+    "threshold": true,
+    "threshold_substitutes": [ "THRESH_CHIMERA" ]
   },
   {
     "type": "mutation",
@@ -8207,7 +8216,8 @@
     "description": "Civilization collapsed?  Great!  You and your kin will never have to worry about a slaughterhouse again.",
     "valid": false,
     "purifiable": false,
-    "threshold": true
+    "threshold": true,
+    "threshold_substitutes": [ "THRESH_CHIMERA" ]
   },
   {
     "type": "mutation",
@@ -8218,7 +8228,8 @@
     "flags": [ "INSECTBLOOD" ],
     "valid": false,
     "purifiable": false,
-    "threshold": true
+    "threshold": true,
+    "threshold_substitutes": [ "THRESH_CHIMERA" ]
   },
   {
     "type": "mutation",
@@ -8229,7 +8240,8 @@
     "flags": [ "PLANTBLOOD" ],
     "valid": false,
     "purifiable": false,
-    "threshold": true
+    "threshold": true,
+    "threshold_substitutes": [ "THRESH_CHIMERA" ]
   },
   {
     "type": "mutation",
@@ -8249,7 +8261,8 @@
     "description": "Not much point to rebuilding up in that horribly bright, roofless wasteland.  Now that you've become accustomed to your new digs, there's the beginning of a great empire right here, underground.",
     "valid": false,
     "purifiable": false,
-    "threshold": true
+    "threshold": true,
+    "threshold_substitutes": [ "THRESH_CHIMERA" ]
   },
   {
     "type": "mutation",
@@ -8260,7 +8273,8 @@
     "flags": [ "INVERTEBRATEBLOOD" ],
     "valid": false,
     "purifiable": false,
-    "threshold": true
+    "threshold": true,
+    "threshold_substitutes": [ "THRESH_CHIMERA" ]
   },
   {
     "type": "mutation",
@@ -8271,7 +8285,8 @@
     "flags": [ "INSECTBLOOD" ],
     "valid": false,
     "purifiable": false,
-    "threshold": true
+    "threshold": true,
+    "threshold_substitutes": [ "THRESH_CHIMERA" ]
   },
   {
     "type": "mutation",
@@ -8281,7 +8296,8 @@
     "description": "Hey.  Civilization fell.  You're still around.  'Rat' just isn't respectful.",
     "valid": false,
     "purifiable": false,
-    "threshold": true
+    "threshold": true,
+    "threshold_substitutes": [ "THRESH_CHIMERA" ]
   },
   {
     "type": "mutation",
@@ -8319,6 +8335,7 @@
     "name": { "str": "Chaos" },
     "points": 1,
     "description": "You can't tell what you are anymore.  Everything and yet nothing, like you weren't meant to exist.  But you do, and you're a force, no matter what happens.",
+    "//": "Acceptable substitute for all lines except the human-based ones and slime - the former are more controlled, the latter will diverge too much in anatomy.",
     "valid": false,
     "purifiable": false,
     "threshold": true
@@ -8331,7 +8348,8 @@
     "description": "The chance to undo not one but TWO extinction events.  You're confident you'll do fine.",
     "valid": false,
     "purifiable": false,
-    "threshold": true
+    "threshold": true,
+    "threshold_substitutes": [ "THRESH_CHIMERA" ]
   },
   {
     "type": "mutation",
@@ -8341,7 +8359,8 @@
     "description": "A perfect ambush predator, if only there were less competition.",
     "valid": false,
     "purifiable": false,
-    "threshold": true
+    "threshold": true,
+    "threshold_substitutes": [ "THRESH_CHIMERA" ]
   },
   {
     "type": "mutation",
@@ -8351,7 +8370,8 @@
     "description": "So much food, everywhere!  And nobody's even guarding it anymore!  These are good times.",
     "valid": false,
     "purifiable": false,
-    "threshold": true
+    "threshold": true,
+    "threshold_substitutes": [ "THRESH_CHIMERA" ]
   },
   {
     "type": "mutation",
@@ -8386,7 +8406,8 @@
     "flags": [ "INVERTEBRATEBLOOD" ],
     "valid": false,
     "purifiable": false,
-    "threshold": true
+    "threshold": true,
+    "threshold_substitutes": [ "THRESH_CHIMERA" ]
   },
   {
     "type": "mutation",
@@ -8396,7 +8417,8 @@
     "description": "You long for a colony, the cover of darkness, and a meal on the wing.",
     "valid": false,
     "purifiable": false,
-    "threshold": true
+    "threshold": true,
+    "threshold_substitutes": [ "THRESH_CHIMERA" ]
   },
   {
     "type": "mutation",
@@ -8884,6 +8906,17 @@
     "enchantments": [ "ENCH_DEBUG_BIG_HEAD" ],
     "debug": true
   },
+  {
+    "type": "mutation",
+    "id": "DEBUG_MUTATE",
+    "name": { "str": "Debug Genetic Instability" },
+    "points": 99,
+    "valid": false,
+    "description": "You just can't wait to turn into a bug!  Triggers a mutation using the normal mutation rules (requiring primer but no catalyst) every five seconds.",
+    "debug": true,
+    "processed_eocs": [ "eoc_debug_mutate" ],
+    "time": "5 s"
+  },
   {
     "type": "mutation",
     "id": "DEBUG_NIGHTVISION",
diff --git a/doc/MUTATIONS.md b/doc/MUTATIONS.md
index ad61f3680ee98..a5fc3b13e6104 100644
--- a/doc/MUTATIONS.md
+++ b/doc/MUTATIONS.md
@@ -105,7 +105,9 @@ Note that **all new traits that can be obtained through mutation must be purifia
   "profession": true,                         // Trait is a starting profession special trait (default: false).
   "debug": false,                             // Trait is for debug purposes (default: false).
   "dummy": false,                             // Dummy mutations are special; they're not gained through normal mutating, and will instead be targeted for the purposes of removing conflicting mutations
-  "threshold": false                          //True if it's a threshold itself, and shouldn't be obtained *easily*.
+  "threshold": false,                         //True if it's a threshold itself, and shouldn't be obtained *easily*.  Disallows mutating this trait directly
+  "threshold_substitutes": [ "FOO", "BAR" ],   // The listed traits are accepted in place of this threshold trait for the purposes of gaining post-threshold mutations
+  "strict_thresreq": false,                   // This trait needs an *exact* threshold match (ie. ignores threshold substitutions)
   "player_display": true,                     // Trait is displayed in the `@` player display menu and mutations screen.
   "vanity": false,                            // Trait can be changed any time with no cost, like hair, eye color and skin color.
   "variants": [                               // Cosmetic variants of this mutation.
diff --git a/src/mutation.cpp b/src/mutation.cpp
index 377046d82dc8e..3ada1e2f599fa 100644
--- a/src/mutation.cpp
+++ b/src/mutation.cpp
@@ -1636,6 +1636,19 @@ bool Character::mutate_towards( const trait_id &mut, const mutation_category_id
                            threshreq[i].c_str() );
             c_has_threshreq = true;
         }
+        for( const trait_id &subst : threshreq[i]->threshold_substitutes ) {
+            if( has_trait( subst ) ) {
+                add_msg_debug( debugmode::DF_MUTATION, "mutate_towards: substitute threshold %s found",
+                               subst.c_str() );
+                if( mdata.strict_threshreq ) {
+                    add_msg_debug( debugmode::DF_MUTATION,
+                                   "mutate_towards: ...but no threshold substitutions allowed for trait %s",
+                                   subst.c_str(), mdata.name() );
+                    continue;
+                }
+                c_has_threshreq = true;
+            }
+        }
     }
 
     // No crossing The Threshold by simply not having it
diff --git a/src/mutation.h b/src/mutation.h
index 9aba84538f072..a4573809bf5e7 100644
--- a/src/mutation.h
+++ b/src/mutation.h
@@ -179,6 +179,10 @@ struct mutation_branch {
         bool purifiable = false;
         // True if it's a threshold itself, and shouldn't be obtained *easily* (False by default).
         bool threshold = false;
+        // Other threshold traits that are taken as acceptable replacements for this threshold
+        std::vector<trait_id> threshold_substitutes;
+        // Disallow threshold substitution for this trait in particular
+        bool strict_threshreq = false;
         // True if this is a trait associated with professional training/experience, so profession/quest ONLY.
         bool profession = false;
         // True if the mutation is obtained through the debug menu
diff --git a/src/mutation_data.cpp b/src/mutation_data.cpp
index bd3750e81e631..1ef7f1716a56f 100644
--- a/src/mutation_data.cpp
+++ b/src/mutation_data.cpp
@@ -367,6 +367,8 @@ void mutation_branch::load( const JsonObject &jo, const std::string &src )
     }
 
     optional( jo, was_loaded, "threshold", threshold, false );
+    optional( jo, was_loaded, "threshold_substitutes", threshold_substitutes );
+    optional( jo, was_loaded, "strict_threshreq", strict_threshreq );
     optional( jo, was_loaded, "profession", profession, false );
     optional( jo, was_loaded, "debug", debug, false );
     optional( jo, was_loaded, "player_display", player_display, true );
diff --git a/tests/mutation_test.cpp b/tests/mutation_test.cpp
index ebfabb5105fd3..ab873941917f0 100644
--- a/tests/mutation_test.cpp
+++ b/tests/mutation_test.cpp
@@ -17,6 +17,7 @@ static const effect_on_condition_id effect_on_condition_changing_mutate2( "chang
 static const morale_type morale_perm_debug( "morale_perm_debug" );
 
 static const mutation_category_id mutation_category_ALPHA( "ALPHA" );
+static const mutation_category_id mutation_category_BIRD( "BIRD" );
 static const mutation_category_id mutation_category_CHIMERA( "CHIMERA" );
 static const mutation_category_id mutation_category_FELINE( "FELINE" );
 static const mutation_category_id mutation_category_HUMAN( "HUMAN" );
@@ -26,6 +27,8 @@ static const mutation_category_id mutation_category_RAPTOR( "RAPTOR" );
 static const mutation_category_id mutation_category_REMOVAL_TEST( "REMOVAL_TEST" );
 static const mutation_category_id mutation_category_TROGLOBITE( "TROGLOBITE" );
 
+static const trait_id trait_BEAK( "BEAK" );
+static const trait_id trait_BEAK_PECK( "BEAK_PECK" );
 static const trait_id trait_EAGLEEYED( "EAGLEEYED" );
 static const trait_id trait_FELINE_EARS( "FELINE_EARS" );
 static const trait_id trait_GOURMAND( "GOURMAND" );
@@ -34,6 +37,7 @@ static const trait_id trait_QUICK( "QUICK" );
 static const trait_id trait_SMELLY( "SMELLY" );
 static const trait_id trait_STR_UP( "STR_UP" );
 static const trait_id trait_STR_UP_2( "STR_UP_2" );
+static const trait_id trait_STR_ALPHA( "STR_ALPHA" );
 static const trait_id trait_TEST_OVERMAP_SIGHT_5( "TEST_OVERMAP_SIGHT_5" );
 static const trait_id trait_TEST_OVERMAP_SIGHT_MINUS_10( "TEST_OVERMAP_SIGHT_MINUS_10" );
 static const trait_id trait_TEST_REMOVAL_0( "TEST_REMOVAL_0" );
@@ -42,7 +46,11 @@ static const trait_id trait_TEST_TRIGGER( "TEST_TRIGGER" );
 static const trait_id trait_TEST_TRIGGER_2( "TEST_TRIGGER_2" );
 static const trait_id trait_TEST_TRIGGER_2_active( "TEST_TRIGGER_2_active" );
 static const trait_id trait_TEST_TRIGGER_active( "TEST_TRIGGER_active" );
+static const trait_id trait_THRESH_ALPHA( "THRESH_ALPHA" );
+static const trait_id trait_THRESH_BIRD( "THRESH_BIRD" );
+static const trait_id trait_THRESH_CHIMERA( "THRESH_CHIMERA" );
 static const trait_id trait_UGLY( "UGLY" );
+static const trait_id trait_WINGS_BIRD( "WINGS_BIRD" );
 
 static const vitamin_id vitamin_mutagen( "mutagen" );
 static const vitamin_id vitamin_mutagen_human( "mutagen_human" );
@@ -723,3 +731,42 @@ TEST_CASE( "The_mutation_flags_are_associated_to_the_corresponding_base_mutation
     verify_mutation_flag( dummy, "COLDBLOOD4", "ECTOTHERM" );
 }
 
+// Test that threshold substitutes work
+// Tested using Chimera for the mainline use case
+TEST_CASE( "Threshold_substitutions", "[mutations]" )
+{
+    Character &dummy = get_player_character();
+    clear_avatar();
+    // Check our assumptions
+    const std::vector<trait_id> bird_subst = trait_THRESH_BIRD->threshold_substitutes;
+    const std::vector<trait_id> alpha_subst = trait_THRESH_ALPHA->threshold_substitutes;
+    REQUIRE( std::find( bird_subst.begin(), bird_subst.end(),
+                        trait_THRESH_CHIMERA ) != bird_subst.end() );
+    REQUIRE( std::find( alpha_subst.begin(), alpha_subst.end(),
+                        trait_THRESH_CHIMERA ) == alpha_subst.end() );
+    REQUIRE( !trait_BEAK_PECK->threshreq.empty() );
+    REQUIRE( !trait_WINGS_BIRD->threshreq.empty() );
+    REQUIRE( !trait_BEAK_PECK->strict_threshreq );
+    REQUIRE( trait_WINGS_BIRD->strict_threshreq );
+
+    // Character tries to gain post-thresh traits
+    for( int i = 0; i < 10; i++ ) {
+        dummy.mutate_towards( trait_BEAK_PECK, mutation_category_BIRD, nullptr, false, false );
+        dummy.mutate_towards( trait_WINGS_BIRD, mutation_category_BIRD, nullptr, false, false );
+        dummy.mutate_towards( trait_STR_ALPHA, mutation_category_ALPHA, nullptr, false, false );
+    }
+    // We didn't gain any, filled up on prereqs though
+    CHECK( !dummy.has_trait( trait_BEAK_PECK ) );
+    CHECK( !dummy.has_trait( trait_WINGS_BIRD ) );
+    CHECK( !dummy.has_trait( trait_STR_ALPHA ) );
+    CHECK( dummy.has_trait( trait_BEAK ) );
+    // After gaining Chimera we can mutate a fancy beak, but no wings or Alpha traits
+    dummy.set_mutation( trait_THRESH_CHIMERA );
+    dummy.mutate_towards( trait_BEAK_PECK, mutation_category_BIRD, nullptr, false, false );
+    dummy.mutate_towards( trait_WINGS_BIRD, mutation_category_BIRD, nullptr, false, false );
+    dummy.mutate_towards( trait_STR_ALPHA, mutation_category_ALPHA, nullptr, false, false );
+    CHECK( dummy.has_trait( trait_BEAK_PECK ) );
+    CHECK( !dummy.has_trait( trait_WINGS_BIRD ) );
+    CHECK( !dummy.has_trait( trait_STR_ALPHA ) );
+}
+